1. Field of Invention
The present invention is concerned broadly with a driving tool for providing rotational motion to a fastener or the like, and to the particular fastener for use in combination with the driving tool. In its more particular aspects, the invention is concerned with a threaded fastener such as a screw and the driving tool to drive or withdraw such a fastener.
2. Description of the Prior Art
Those using screwdrivers of ordinary construction, e.g., a blade whose bottom is flat and comprising converging planar side faces terminating at the flat bottom, are accustomed to the driver slipping out of the nick in the head of the screw particularly when the nick in the screw is a conventionally shaped nick or slot and the screw is somewhat difficult to turn, as during the last few turns in driving the screw into a workpiece or in starting the screw in taking it out, and especially if the nick or groove of the screw, or the tip of the screwdriver, is in the least bit worn.
As a result of this slippage the greater part of the force exerted in screwing a screw in or out is often expended in maintaining the screwdriver in engagement with the screw. Unless axial pressure, and sometimes very great pressure, is applied to the screwdriver, its operating end may repeatedly slip out over the walls of the nick or groove in the screw head, involving not only a loss of time and energy in re-applying the screwdriver to the screw, but increasing the probability of injury to an operator's hands and fingers.
Oftentimes the surface of the material containing the screw is scratched and marred by the slipping of the screwdriver blade. These difficulties with screwdriver slippage become quite serious in some cases, e.g., working with finished hard wood constructions, as the slippage of the screwdriver results in scratches or disfigurement, which cannot be readily removed, if at all.
Moreover, after a screwdriver has once slipped from the nick of a screw, it becomes more difficult to prevent its recurrence, owing to the fact that the edge of the nick becomes somewhat rounded off and offers less resistance to slippage. The more times the blade slips, the more rounded the nick walls become, making it even more difficult to screw or unscrew the screw. This is particularly a noticeable problem in the case of soft metal screws, e.g., screws of brass, aluminum, copper, etc.
In certain uses, e.g., in overhead work and in placing screws in vertical locations, it is also most difficult to start a screw with the ordinary screwdriver. This is because the screwdriver and screw are separate and distinct from one another and in no way are fastened together. The particular location, moreover, may prevent an operator, in starting the screw into the work, from properly holding the screw in his one hand while operating the driving tool with the other. As a result, the screw may be repeadedly dropped, requiring repeated reapplication and making for a more difficult, tiring, frustrating, and time consuming operation. This is particularly bothersome when the operator may be on a ladder. In this case, if the operator is a home owner, he may have to descend the ladder to locate the screw. Sometimes the screw cannot be readily located and is even lost. If the operator is involved in an industrial operation, the fallen screw is not ordinarily retrieved; the operator merely takes another screw from his supply. The fallen screw may eventually be swept away, but meanwhile it sometimes presents an unsafe condition, and like the proverbial banana peel can result in a slip and fall injury if someone steps on it.
Over the years, various screwdrivers and screws have been devised as a solution to the problems pointed out above, as exemplified in U.S. Pat. Nos. 132,946; 685,197; 1,055,031; 1,056,095; 1,366,341; 1,797,390; 1,997,422; 2,301,590; 3,923,088; 4,016,912; and 4,078,593. In U.S. Pat. No. 132,946, there is disclosed a screw in which an undercut nick is provided in the screw head, and in which the nick widens from the center to the head circumference. The screwdriver for the screw has a blade made of two parts for being wedged into the nick from each end to the center of the screw. Thus, the screw is fastened to the end of the driver facilitating presentation of the screw in overhead work.
The invention disclosed in U.S. Pat. Nos. 685,197; 1,055,031; and 1,056,095 are to improved screwdrivers. In the first patent, the invention comprises a screwdriver in which the blade portion entering the nick or groove of the screw is provided with projections extending laterally in opposite directions. These projections, as disclosed by the patentee, are to be sufficiently sharp so that they bite into the walls of the nick on opposite sides, preventing the screwdriver from slipping out of the nick. The terminal portion of the screwdriver in U.S. Pat. Nos. 1,055,031; and 1,056,095 is provided with grooves that increase in depth and width from the center to the edge of the blade. Thus, a sharp point or tooth is provided for engaging the wall of the nick in the screw head. As shown in U.S. Pat. No. 1,056,095, such a screwdriver can be used in conjunction with a screw in the head of which is provided a nick or groove having overhanging or beveled sides.
U.S. Pat. No. 1,366,341 discloses a screw the head of which is provided with a nick which can be of dove-tail configuration. The screwdriver blade tip is of complementary configuration and is provided with a longitudinal slidable shell that engages the screw head, locking the screwdriver in combination with the screw.
In U.S. Pat. No. 1,797,390, there is disclosed a screwdriver designed to be keyed on a screw. As shown in that patent, the bit of the driver is provided with a key that intrudes into a longitudinal slot in the screw, thereby centering the screwdriver in the nick or the cross slot of the screw. The driver bit tapers laterally from the key to the outer edges of the blade enabling easy access of the bit in the cross-slot while the driving tool is revolved.
U.S. Pat. No. 1,997,422 discloses a screw and screwdriver permitting interlocking engagement between the two. The screw head is provided with a slot that is bigger at the bottom than at the top. Thus, when the screwdriver is inserted into the end of the slot and aligned, its bit, being of a complementary shape, is prevented from accidental disengagement.
U.S. Pat. No. 2,301,590 shows a screwdriver whose bit comprises two resilient beveled members. After the two beveled members are engaged with the dove-tail shaped slot in the associated screw, the shanks associated with the beveled members are operated to make them inflexible whereby the beveled members are interlocked with the screw.
In U.S. Pat. No. 3,923,088, there is disclosed a biting screwdriver having a foot portion on the lower extremity of its blade for increasing the effectiveness of the blade in gripping the side walls of a screw nick or slot. The driver is used with conventional screws having a nick comprising planar, parallel, vertical, spaced-apart walls.
U.S. Pat. No. 4,016,912 discloses a screwdriver for slotted-head screws in which the screwdriver bit is provided with protuberances on opposite sides thereof to engage the walls of a dull or deformed slot of a slotted-head screw, to hold the screwdriver against undesirable shifting lengthwise of the slot in screwing and unscrewing the screw.
In U.S. Pat. No. 4,078,593 there is disclosed a screwdriver comprising a shank comprising two elements and a slide mechanism. The slide mechanism acts to expand and contract the shank elements to thicken and thin the screwdriver blade formed by the tips of the shank elements, as desired. Thus, screw slots can be more readily engaged, particularly if a portion of the slot is occludded.
While the various screwdrivers and associated screws as disclosed in the above patents may provide satisfactory performance to a certain degree, their apparent lack of commercial availability would seem to indicate their performance is not totally satisfactory. This may be due not only to the rather complicated nature of certain of the driving tools, but also to a variety of other reasons. In many instances, the driver bits and screw configuration do not really provide for satisfactory interlocking engagement. This is due to the fact that in many instances the nick and bit are of complementary cross-section. Thus, this "mating configuration", does not really permit a wedging of one with the other to occur. In other instances the sharp edge provided on the foot of the driver blade does not actually cut into the side wall of the nick, and when no cut is made into the side wall, no interlock can really be provided. Even when a cut is made in a nick side wall, there is really no interlocking engagement between the screwdriver and screw as they are easily separated. In some cases the driver has to be inserted into the screw nick from the edge of the screw; or has to be manipulated from the vertical to gain entry to the nick, or to be retracted from it. Thus, some of the driving tools cannot be used at all with countersunk holes.